This application claims the benefit of Korean Patent Application No. 2000-0063915, filed on Oct. 30, 2000 in Korea, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display (LCD) device having a color filter substrate and manufacturing method thereof.
2. Discussion of the Related Art
Generally, typical thin film transistor liquid crystal display (TFT-LCD) devices include an upper substrate and a lower substrate with liquid crystal molecules interposed therebetween. The upper substrate and the lower substrate are generally referred to as a color filter substrate and an array substrate, respectively. The upper substrate and the lower substrate respectively include electrodes disposed on opposing surfaces of the upper substrate and the lower substrate. An electric field is generated by applying a voltage to the electrodes, thereby driving the liquid crystal molecules to display images depending on light transmittance.
In accordance with the application of an internal or external light source, LCD devices are commonly classified into two categories: a transmission type and a reflection type. The transmission type LCD has a liquid crystal display panel that does not emit light, and therefore, a backlight is provided to function as a light-illuminating source. The backlight is disposed at a first or rear side of the panel, and light emitted from the backlight passes through the liquid crystal panel to be controlled by the liquid crystal panel, thereby displaying an image. That is, the liquid crystal panel display forms an image according to an arrangement of the liquid crystal molecules that transmit or interrupt light emitted from the backlight. However, the backlight of the transmission type LCD consumes 50% or more of the total power consumed by the LCD device. Accordingly, the use of the backlight increases power consumption of the LCD device.
To reduce power consumption, reflection type LCD devices have been developed for portable information apparatuses that are often used outdoors or carried along with users. Such reflection type LCD devices are provided with a reflector formed on one of a pair of substrates, and ambient light is reflected from the surface of the reflector. However, visibility of the display of reflection type LCD devices is extremely poor when the surrounding environment is dark and no ambient light is available.
In order to overcome the above problems, a transflective liquid crystal display device has been proposed that utilizes both transmissive and reflective mode displays in a single liquid crystal display device. The transflective liquid crystal display (LCD) device alternatively acts as a transmissive LCD device and a reflective LCD device by making use of both internal and external light sources, thereby providing operation with low power consumption in good ambient light conditions.
FIG. 1 is a schematic cross-sectional view showing a layer structure of a typical transflective LCD device.
As shown, the transflective LCD device includes upper and lower substrates 30 and 10 and a horizontally oriented liquid crystal layer 60 interposed therebetween. The lower substrate 10 has a thin film transistor (TFT) (not shown) and a pixel electrode 20 disposed on the surface facing the upper substrate 30. The pixel electrode 20 includes reflective electrode portions 22 and a transparent electrode portion 21 disposed in an opening therebetween. The transparent electrode 21 is formed of ITO (indium-tin-oxide) or IZO (indium-zinc-oxide) having high light transmittance, and the reflective electrode 21 is made of aluminum (Al) having low electrical resistance and superior light reflectance.
The upper substrate 30 includes a color filter 40 formed on the surface facing the lower substrate 10 corresponding to the pixel electrode 20, and a common electrode 50 formed on the color filter 40.
Furthermore, first and second retardation films 71 and 72 are formed on outer surfaces of the lower and upper substrates 10 and 30, respectively. The first and second retardation films 71 and 72 are quarter wave plates (QWPs). The first and second QWPs 71 and 72 change a polarization state of light transmitted through the liquid crystal layer 60, specifically, convert linearly polarized light into right- or left-handed circularly polarized light, and conversely convert right- or left-handed circularly polarized light into linearly polarized light. Lower and upper polarizers 81 and 82 are formed on each outer surface of the first and the second QWPs 71 and 72, respectively. Here, a polarization axis of the upper polarizer 82 makes an angle of 90 degrees with a polarization axis of the lower polarizer 81. Furthermore, a backlight device 90 is disposed adjacent to the lower polarizer 81 and functions as a light source in the transmissive mode.
However, since the transflective LCD device is designed on the basis of the reflective mode, the transmittance of the transmissive mode is only about 50% of that of the reflective mode without the applying voltage the liquid crystal layer. Therefore, the transmittances of the reflective and transmissive modes can be the same by making the liquid crystal layer of the transmissive area thicker than that of the reflective area.
FIG. 2 is a schematic cross-sectional view showing the array substrate of the transflective LCD device as described above.
The region of the array substrate is divided into transmissive and reflective areas. As shown, the gate electrode 121 is patterned on the insulating substrate 110 and the gate insulator 130 is formed thereon. The active layer 140 of amorphous silicon is patterned on the gate insulator 130 and the source and drain electrodes 151 and 152 are patterned thereon. The ohmic contact layer (not shown) is interposed between the active layer 140 and the source and drain electrodes 151 and 152. The source and drain electrodes 151 and 152 are covered with the first passivation layer 160 of the organic insulator, which includes the first contact hole 161 that exposes the drain electrode 152 and the first transmissive hole 162 at the position corresponding to the transmissive area. Since the liquid crystal layer of the transmissive area is thicker than that of the reflective area due to the first transmissive hole 162, the brightness of the transmissive and reflective modes can be made uniform. It is desirable to make the thickness of the transmissive area twice as that of the reflective area. The transmissive electrode 170 of the transparent conducting material is patterned on the first passivation layer 160 and connected with the drain electrode 152 through the first contact hole 161. The second passivation layer 180 of a material such as silicon nitride (SiNx) is formed on the transmissive electrode 170 and includes a second contact hole 181 that exposes the transmissive electrode 170 on the first contact hole 161. The reflective electrode 190 is patterned on the second passivation layer 180 and connected with the transmissive electrode 170 through the second contact hole 181. Furthermore, the reflective electrode 190 includes the second transmissive hole 191 that exposes the transmissive electrode 170 on the first transmissive hole 162 and can be made of the aluminous metal of low resistance and high reflectance.
Consequently, in the transflective LCD devices, the transmittance of the transmissive mode can be made nearly the same as that of the reflective mode by forming the hole at the transmissive area of the organic insulator and making the thickness of the liquid crystal layer at the transmissive area twice that at the reflective area.
However, since the thickness of the liquid crystal layer increases by the depth of the first and second contact holes 161 and 181, the light efficiency of the area on the contact holes is reduced. Therefore, the transmittance of the reflective mode decreases.
FIG. 3 shows the transmittance of the reflective mode of the transflective LCD device according to the retardation xcex94n.d. Here, the transmittance means the rate of the reflective light to the incident light.
As shown, since the liquid crystal layer of the area of the contact holes 161, 181 in region xe2x80x9cAxe2x80x9d is thicker than that of any other regions, the retardation xcex94n.d is different and the transmittance of this region is much lower than that of the normal reflective mode. The larger the area of the contact holes 161, 181, the lower the brightness of the reflective mode. Furthermore, considering the fabrication margin, the area of the first contact hole 161 is three or four times that of the second contact hole 181. Therefore, the total brightness of the reflective mode decreases by the decrease of the transmittance due to the depth of the contact holes 161, 181 and the increase of the area of the contact holes 161, 181.
Accordingly, the present invention is directed to a transflective liquid crystal display device and manufacturing method thereof that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a transflective liquid crystal display device and a manufacturing method thereof that has a uniform transmittance both in the reflective and transmissive modes.
Another object of the present invention is to provide a transflective liquid crystal display device and a manufacturing method thereof that has a high brightness in the reflective mode.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an array substrate for a transflective liquid crystal display device includes a substrate, a plurality of thin film transistors formed on the substrate and having gate, source and drain electrodes, a first passivation layer covering the thin film transistors and having a plurality of first contact holes exposing the drain electrodes, a plurality of transparent electrodes formed on the first passivation layer and connected with the drain electrodes through the first contact holes, a second passivation layer formed on the transparent electrodes and having a plurality of second contact holes exposing the transparent electrodes on the first contact holes and a plurality of reflective electrodes formed on the second passivation layer, connected with the transparent electrodes through the second contact holes and having a plurality of first transmissive holes, wherein the first and second passivation layers have different thicknesses and an area of the contact holes in the thicker passivation layer is broader than that of the contact holes in the other passivation layer.
In another aspect of the present invention, an array substrate for a transflective liquid crystal display device includes a substrate, a plurality of thin film transistors formed on the substrate and having gate, source and drain electrodes, a first passivation layer covering the thin film transistors and having a plurality of first contact holes exposing the drain electrodes, a plurality of transparent electrodes formed on the first passivation layer and connected with the drain electrodes through the first contact holes, a second passivation layer formed on the transparent electrodes and having a plurality of second contact holes exposing the transparent electrodes on the other portion of the first contact holes and a plurality of reflective electrodes formed on the second passivation layer, connected with the transparent electrodes through the second contact holes and having a plurality of first transmissive holes, wherein the first and second passivation layers have different thicknesses.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.